5 ms·

Surely any electric brake would fail closed? Just like air-brakes on large trucks. That would make them safer right?

by ollie87 10y ago

cmdrfred 10y ago
As long as actually fails yes, if the switch on the break pedal fails open for example you'd be in a world of hurt. I see where mistakes being made.
- bigtech 10y ago
  They don't have to be perfect -- they just have to fail less often than current technology.
  - deleted 10y ago
    [deleted]
peterwwillis 10y ago
Only truck brakes are designed to fail closed. Passenger vehicles aren't, even though they could be. In fact, there's a lot of safety systems that passenger cars don't have, for no discernible reason. There's no warning light for the brake fluid reservoir or pressure, even though it would be trivial to add. The oil warning light for passenger vehicles is so useless, when it comes on you have to stop your vehicle immediately. Gasoline gauges are designed to trick people into thinking they're on empty and then provide an extra gallon or two, even though they could actually design the gauge to display average miles based on the rated mileage of the car and size of the tank. Transmission, diff, brake, and engine oil fluids could be measured or at least timed for when they need to be replaced and a warning given to the user that it's time to maintain it. Only in modern [usually expensive] cars do you find tire air pressure sensors. Why don't we have these basic maintenance and safety systems built into cars? Too expensive? Too technically challenging? Nope - they want you to bring your car into the dealer regularly to regularly charge you for maintenance you may not need.
- MertsA 10y ago
  >There's no warning light for the brake fluid reservoir or pressure, even though it would be trivial to add. What deathtrap are you driving? This is a common thing. Even my old 96 Camry has it.
  - peterwwillis 10y ago
    Hmm. Well it seems like it's possible the cars i've had have shared the same indicator for multiple brake notifications. But i've not noticed a dedicated light for brake fluid. There's one for the e-brake engagement, and one for ABS, for no particular reason, because it's a non-critical brake feature.... but i've not seen a dedicated brake pressure light.
    - sandworm101 10y ago
      Sometimes they are linked to other systems. My 92 bmw shared the brake fluid reservoir with the clutch. A leak in the clutch triggered the brake warning light.
    - MertsA 10y ago
      On my camry, it is shared with the ebrake light.
  - sandworm101 10y ago
    Even without the warning lights, spongy or soft brakes is something every driver is taught to recognize. That will happen long before total failure.
sandworm101 10y ago
Not on passenger cars. The fail-closed thing is only done on larger vehicles. There is a reason. Fail-on systems have a max applicable force. Basically, they are some sort of spring pushing the brakes on 24/7 and the control system fights against this spring. So when the system fails, the brakes default on. But that means that stamping on the brake pedal harder and harder doesn't translate into greater braking force. The spring sets the max force. That is OK on a truck or train where human muscle is irrelevant, but in a passenger car or motorcycle human muscle is more than enough to lock up the tires (ie go beyond maximum braking potential). Large vehicles also do not have the same performance envelope and so can generally survive a braking system that suddenly fails "on". A truck+trailer can lock its trailer brakes without, normally, going out of control. So too with a train or even an aircraft on landing. If that happened on a motorcycle, the rider would die. No questions, just death. Cars are somewhere in the middle. Some cars could survive but many would become instantly uncontrollable. (Remember there are limitations on antilocks in no-power situations. They cannot antilock forever and so will eventually lock up.)

Surely any electric brake would fail closed? Just like air-brakes on large trucks. That would make them safer right?

by ollie87 10y ago

Surely any electric brake would fail closed? Just like air-brakes on large trucks. That would make them safer right?

As long as actually fails yes, if the switch on the break pedal fails open for example you'd be in a world of hurt. I see where mistakes being made.

bigtech 10y ago
They don't have to be perfect -- they just have to fail less often than current technology.
- deleted 10y ago
  [deleted]

peterwwillis 10y ago

Only truck brakes are designed to fail closed. Passenger vehicles aren't, even though they could be. In fact, there's a lot of safety systems that passenger cars don't have, for no discernible reason. There's no warning light for the brake fluid reservoir or pressure, even though it would be trivial to add. The oil warning light for passenger vehicles is so useless, when it comes on you have to stop your vehicle immediately. Gasoline gauges are designed to trick people into thinking they're on empty and then provide an extra gallon or two, even though they could actually design the gauge to display average miles based on the rated mileage of the car and size of the tank. Transmission, diff, brake, and engine oil fluids could be measured or at least timed for when they need to be replaced and a warning given to the user that it's time to maintain it. Only in modern [usually expensive] cars do you find tire air pressure sensors. Why don't we have these basic maintenance and safety systems built into cars? Too expensive? Too technically challenging? Nope - they want you to bring your car into the dealer regularly to regularly charge you for maintenance you may not need.

MertsA 10y ago
>There's no warning light for the brake fluid reservoir or pressure, even though it would be trivial to add. What deathtrap are you driving? This is a common thing. Even my old 96 Camry has it.
- peterwwillis 10y ago
  Hmm. Well it seems like it's possible the cars i've had have shared the same indicator for multiple brake notifications. But i've not noticed a dedicated light for brake fluid. There's one for the e-brake engagement, and one for ABS, for no particular reason, because it's a non-critical brake feature.... but i've not seen a dedicated brake pressure light.
  - sandworm101 10y ago
    Sometimes they are linked to other systems. My 92 bmw shared the brake fluid reservoir with the clutch. A leak in the clutch triggered the brake warning light.
  - MertsA 10y ago
    On my camry, it is shared with the ebrake light.
- sandworm101 10y ago
  Even without the warning lights, spongy or soft brakes is something every driver is taught to recognize. That will happen long before total failure.

sandworm101 10y ago

Not on passenger cars. The fail-closed thing is only done on larger vehicles. There is a reason. Fail-on systems have a max applicable force. Basically, they are some sort of spring pushing the brakes on 24/7 and the control system fights against this spring. So when the system fails, the brakes default on. But that means that stamping on the brake pedal harder and harder doesn't translate into greater braking force. The spring sets the max force. That is OK on a truck or train where human muscle is irrelevant, but in a passenger car or motorcycle human muscle is more than enough to lock up the tires (ie go beyond maximum braking potential). Large vehicles also do not have the same performance envelope and so can generally survive a braking system that suddenly fails "on". A truck+trailer can lock its trailer brakes without, normally, going out of control. So too with a train or even an aircraft on landing. If that happened on a motorcycle, the rider would die. No questions, just death. Cars are somewhere in the middle. Some cars could survive but many would become instantly uncontrollable. (Remember there are limitations on antilocks in no-power situations. They cannot antilock forever and so will eventually lock up.)